Mechanical maintaining system for a device with a substantially flat element, in particular for liquid crystal display device

ABSTRACT

The invention relates to the field of mechanical holding systems for devices with appreciably flat element. This is a device comprising: at least one appreciable flat element ( 4 ); the surround ( 1 ) intended to receive the element ( 4 ), the surround ( 1 ) comprising two parts ( 2, 3 ) intended to trap a portion of the element ( 4 ) between them in a direction (Y) roughly orthogonal to the mean plane (XZ) of the element ( 4 ) via at least one elastic gasket ( 7, 8 ); a mechanical system for holding the relative position of the parts ( 2, 3 ) of the surround ( 1 ) one with respect to the other; the parts ( 2, 3 ) of the surround ( 1 ) and the mechanical holding system being structured and arranged in such a way as to be able to hold several relative positions of the parts ( 2, 3 ) of the surround ( 1 ) one with respect to the other in a direction (Y) roughly orthogonal to the mean plane (XZ) of the element ( 4 ).  
     The invention is, for example, applied in liquid crystal display devices.

[0001] The invention relates to the field of mechanical holding systemsfor devices involving an appreciably flat element, particularly forliquid crystal display devices. The device comprises one or moreappreciably flat elements. An appreciably flat element is an element ofwhich one of the dimensions, known as the thickness, is smaller than onehalf of each of the other two dimensions which together form the meanplane of the element. The flat element needs to be held mechanicallybetween two parts of the surround of the device using a mechanicalholding system, preferably a demountable one.

[0002] According to a prior art known in the field of liquid crystalscreen display devices, a surround comprising two parts intended to trapthe appreciably flat element via two elastic gaskets is provided. Thetwo parts of the surround are brought into abutment against one anothervia a contact surface parallel to the mean plane of the appreciably flatelement. The two parts of the surround are held one with respect to theother by a clamping device the axis of which is orthogonal to the meanplane of the appreciably flat element. Between the appreciably flatelement and each of the parts of the surround intended to trap theappreciably flat element there is a gasket with a square cross sectionso as to absorb the tolerances in the direction of the thickness of theappreciably flat element.

[0003]FIG. 1 gives an example of such a device according to the priorart. FIG. 1 schematically depicts a sectioned view of a device with anappreciably flat element held mechanically by a system according to theprior art. The appreciably flat element 4 is a liquid crystal screen.

[0004] The screen 4 comprises a top plate 5 and a bottom plate 6 betweenwhich the liquid crystals are arranged. The bottom plate 6 is generallyknown as TFT, while the top plate 5 is generally known as the backelectrode. The useful region of the screen 4 corresponds to the area ofthe top plate 5. The bottom plate 6, which is larger than the top plate5, is held between the two parts of the surround 1, between the upperpart 2 and the lower part 3, respectively, by two gaskets, namely theupper gasket 7 and the lower gasket 8. The mean plane of the screen 1 isthe plane XZ while the direction of the thickness of the screen 1, thatis to say the direction orthogonal to the mean plane XZ of the screen 1is the axis Y. The two, upper 2 and lower 3, parts of the surround 1 arebrought into abutment one against the other via the contact surface SC.The axis a of clamping of the two parts 2 and 3 of the surround togetheris depicted in chain line.

[0005] One disadvantage with this prior art is the difficulty that themechanical holding system has in holding the appreciably flat elementfirmly while at the same time remaining capable of absorbing thetolerances which are sometimes high. The problem is that the holdingforce exerted by the parts of the surround on the appreciably flatelement via the gaskets is uncontrolled, this force depending on thetolerance on the dimensions lying between the two parts of the surroundin a direction orthogonal to the mean plane of the appreciably flatelement. Thus, if the parts of the surround are clamped together hardenough to hold the appreciably flat element firmly when the dimensionsare at a minimum, then when the dimensions are at a maximum there is arisk that the gripping will be too firm either not to damage theappreciably flat element or not to disrupt its operation when theappreciably flat element is fragile, which is the preferred case of aliquid crystal screen the image displayed on which may be degraded, forexample exhibiting white areas, or not to damage the gasket or gasketssituated between the appreciably flat element and the surround; and viceversa. An appreciably flat element held too loosely carries the risk ofbeing damaged as, for example, a liquid crystal screen subjected to highlevels of vibration carries the risk of the vibration shearing off itselectrical connections to the rest of the device. The troublesomevibrations are especially transverse vibrations, that is to sayvibrations in the mean plane of the appreciably flat element, ratherthan vibrations orthogonal to the mean plane of the appreciably flatelement. For an elastic gasket to play its part correctly, it needs tobe compressed neither too much nor too little.

[0006] The invention proposes a solution in which the force with whichthe appreciable flat element is held by the parts of the surround via atleast one elastic gasket is controlled. Thus, the compromise reachedbetween, on the one hand, sufficiently firm holding of the appreciablyflat element when the dimensions between the two parts of the surroundin a direction orthogonal to the mean plane of the appreciably flatelement are at a minimum and, on the other hand, avoiding excessivecrushing either of the gasket or of the appreciably flat element whenthe dimensions lying between the two parts of the surround a directionorthogonal to the mean plane of the appreciably flat element are at amaximum, is far better.

[0007] According to the invention, there is provided a device comprisingat least an appreciably flat element; a surround intended to receive theelement, the surround comprising two parts intended to trap a portion ofthe element between them in a direction roughly orthogonal to the meanplane of the element via at least one elastic gasket; a mechanicalsystem for holding the relative position of the parts of the surround,one with respect to the other; characterized in that the parts of thesurround and the mechanical holding system are structured and arrangedin such a way as to be able to hold several relative positions of theparts of the surround, one with respect to the other, in a directionroughly orthogonal to the mean plane of the element.

[0008] The invention will be better understood and other features andadvantages will become apparent with the aid of the descriptionhereinafter and of the appended drawings which are given by way ofexample in which:

[0009]FIG. 1 schematically depicts a sectioned view of a deviceinvolving an appreciably flat element held mechanically by a systemaccording to the prior art;

[0010]FIG. 2 schematically depicts a sectioned view of a preferredembodiment of a device involving an appreciably flat element heldmechanically by a system according to the invention;

[0011]FIG. 3 schematically depicts a side view of an advantageous detailof a device involving an appreciably flat element held mechanically by asystem according to the invention;

[0012]FIG. 4 schematically depicts a sectioned view of anotheradvantageous detail of a device involving an appreciably flat elementheld mechanically by a system according to the invention.

[0013] The device comprises an appreciably flat element which will needto be held firmly between the two parts of a surround without, however,being crushed. In all of the text which follows, when we speak of theparts of the surround without qualifying this term in any way, we arespeaking, unless mentioned otherwise, about those parts of the surroundwhich are intended to trap the appreciably flat element. In all the textwhich follows, we shall speak of the appreciably flat element or of theliquid crystal screen, but it is not excluded for the device accordingto the invention to have several of these, it being possible for thevarious appreciably flat elements to be held by just one or several setsof different surround parts. The device also comprises a surroundintended to receive the appreciably flat element, the surroundcomprising two parts intended to trap a portion of the appreciably flatelement between them in a direction roughly orthogonal to the mean planeof the appreciably flat element via at least one elastic gasket. Thesurround comprises at least two parts whose purpose is to be able totrap the appreciably flat element between them, it being possible forthe surround to have several other parts. Trapping is achieved in adirection roughly orthogonal to the mean plane of the appreciably flatelement, like in the prior art, the ideal being an orthogonal directionbecause the less orthogonal the direction, the more lateral loading willbe placed on the elastic gasket or gaskets thus deforming themlaterally, which is bad for the device as a whole and carries the riskof damaging or disrupting its operation. Trapping is via at least oneelastic gasket arranged between the appreciably flat element and one ofthe parts of the surround, a plasticized film being, for example, placedbetween the appreciably flat element and the other part of the surround,or alternatively via two elastic gaskets, each interface between theappreciably flat element and the surround being occupied by an elasticgasket. An elastic gasket is a gasket which can be compressed by force.A portion of the appreciably flat element is trapped, and this portionis preferably its periphery. To go all around the periphery of theappreciably flat element, the elastic gasket or gaskets are either madeas a single piece or in several sections depending on the productionconstraints imposed by the type of appreciably flat element anticipated.The device also comprises a mechanical system for holding the relativeposition of the parts of the surround one with respect to the other soas to be able to keep the appreciably flat element trapped.

[0014] Whereas in the prior art, the parts of the surround and themechanical holding system were structured and arranged in such a waythat the parts of the surround butted against each other, this abutmentposition being the only relative position of the parts of the surroundone with respect to the other in a direction roughly orthogonal to themean plane of the appreciably flat element, in the invention the partsof the surround and the mechanical holding system are structured andarranged in such a way as to be able, in a direction roughly orthogonalto the mean plane of the appreciably flat element, to hold severalrelative positions of the parts of the surround one with respect to theother. By virtue of the different relative positions of the parts of thesurround one with respect to the other, the mechanical holding systemcan adapt to suit different dimensions lying between the parts of thesurround in a direction orthogonal to the mean plane of the appreciablyflat element, from the minimum dimensions to the maximum dimensions,even if the tolerance band is wide, while at the same time achieving agood compromise between holding the appreciably flat element firmlyenough and avoiding excessive crushing either of the gasket or of theappreciably flat element. For this compromise to be reached, a suitablenominal force merely needs to be applied between the parts of thesurround, at the time of mounting, in a direction orthogonal to the meanplane of the appreciably flat element, until this force is balanced bythe compression of the elastic gasket or gaskets, that is to say by theopposing force supplied by the compressed gasket or gaskets. Variouspositions, provided they are close enough together and cover asufficiently large range, allow the force actually applied to be veryclose to the desired nominal force, as close as desired because for thatall that is required is for the distance between two adjacent positionsto be reduced, even in the event of a wide tolerance on the dimensionsbetween the parts of the surround. The various relative positionspreferably cover at least one continuos range so that the force actuallyapplied can be roughly equal to the desired nominal force. Setting theappropriate degree of trapping of the appreciably flat element which inthe prior art depended on a collection of one or several mechanicaldimensions that were expensive to control, but in the invention dependson the application of a force which is far easier to control.

[0015] The device is preferably a display device and the appreciablyflat element is preferably an appreciably flat display cell. Theappreciably flat display cell is advantageously a liquid crystal screen.In the preferred numerical example of the invention, between the twoparts of the surround intended to trap the liquid crystal screen, thestring of dimensions is approximately 2.7 mm±0.5 mm, namely a differencebetween the string of minimum dimensions and the string of maximumdimensions of about 1 mm. Now, one or two gaskets with a total thicknessof 1.6 mm should be compressed between 10% and 30% of their thickness inorder to play their part optimally, and this corresponds to a variationof at most 20% of 1.6 mm, that is to say about 0.3 mm, which is a valuewell below the 1 mm that typifies the difference between the strings ofminimum and maximum dimensions, and which by way of example illustratesthe benefit of the invention.

[0016] In a preferred embodiment, in order to allow the parts of thesurround to have several relative positions one with respect to theother, the parts of the surround intended to trap the appreciably flatelement between them, in a held position, have at least one contactsurface roughly orthogonal to the mean plane of the appreciably flatelement. Optimally, the contact surface is exactly orthogonal to themean plane of the appreciably flat element, because the only forceexerted on the elastic gasket or gaskets is a force exactly orthogonalto the mean plane of the appreciably flat element, whereas as thecontact surface becomes less orthogonal to the mean plane of theappreciably flat element, a component of force tangential to the meanplane of the appreciably flat element tends increasingly to be exertedon the elastic gasket or gaskets, carrying an increasing risk ofdamaging them. The proportion of tangential force that the elasticgasket or gaskets used can take before they are significantly damageddepends on the type of elastic gasket used and therefore on the type ofappreciably flat element considered. To allow the various aforementionedrelative positions all to be actually reached, the parts of the surroundpreferably have no parallel contact surface within the range of theaforementioned relative positions, when their relative movement causesthem to cover said range, because if they did, part of said range wouldnot be able to be used. Other embodiments are possible, for example acommon rail the direction of which is roughly orthogonal to the meanplane of the appreciably flat element, and on which common rail the twoparts of the surround can move in order to trap the appreciably flatelement.

[0017]FIG. 2 schematically depicts a sectioned view of one preferredembodiment of a device involving an appreciably flat element heldmechanically by a system according to the invention. Like FIG. 1, FIG. 2depicts only the surround and the gaskets on the left-hand side of thescreen 4, it being understood that the surround and the gaskets may alsotrap the right-hand side of the screen 4, or even, for example, trap theentire periphery of the screen 4. The appreciably flat element depictedcorresponds to a liquid crystal screen 4 comprising a top plate 5 and abottom plate 6. The useful region of the screen 4 corresponds to thearea of the top plate 5. The screen 4 is trapped by the upper 2 andlower 3 parts of the surround 1 via upper 7 and lower 8 elastic gaskets.The gaskets 7 and 8 preferably have a rectangular cross section. Thegaskets 7 and 8 have a width 1 and a thickness e which are respectivelythe length and the width of the rectangular cross section. Between theupper part 2 of the surround 1 and the screen 4 (or more specificallythe bottom plate 3 of the screen 4) there is the upper elastic gasket 7.Between the lower part 3 of the surround 1 and the screen 4 (or morespecifically the bottom plate 3 of the screen 4) is the lower elasticgasket 8. The upper 2 and lower 3 parts of the surround 1 have a contactsurface SC which is parallel to the axis Y, that is to say which isroughly orthogonal to the mean plane of the screen 4 which is parallelto the plane XZ. There is no contact surface for contact between theupper 2 and lower 3 parts of the surround 1 which is parallel to themean plane of the screen 4. The upper 2 and lower 3 parts of thesurround are held in position one with respect to the other by aclamping device described later on in conjunction with FIGS. 3 and 4 andthe axis of clamping s of which is orthogonal to the axis of compressionof the upper 7 and lower 8 elastic gaskets, said axis of compressionbeing parallel to the axis Y. The axis of clamping S is depicted inchain line. The upper part 2 of the surround 1 has a surface S2 facingthe lower part 3 of the surround 1, while the lower part 3 of thesurround 1 has a surface S3 facing the upper part 2 of the surround 1.The surfaces S2 and S3 both advantageously have a stepped profile. Thecontact surface SC is the contact surface common to the surfaces S2 andS3.

[0018] The mechanical holding system is preferably a clamping devicecomprising at least one screw sliding in an oblong hole. This clampingdevice advantageously comprises a washer arranged between the screw andthe oblong hole, the washer being large enough to increase the area overwhich the screw bears against the oblong hole. This oblong holepreferably lies in a depression which is located in an outer surface ofthe surround and which is arranged toward the inside of the device.Thus, the clamping device occupies less space and the ratio between theuseful region of the appreciably flat element and the total area of theappreciably flat element is increased. Other holding systems may be usedto hold the relative position of the two parts of the surround withrespect to each other.

[0019]FIG. 3 schematically depicts a side view of an advantageous detailinvolving the device for clamping the parts of the surround of a deviceinvolving an appreciably flat element held mechanically by a systemaccording to the invention. The outer surface 10 of the surround 1, morespecifically the outer surface 10 of the upper part 2 of the surround 1has an oblong hole 11 through which there passes a clamping screw 12which can be screwed into the lower part 3 of the surround 1. The rolesof the upper 2 and lower 3 parts of the surround 1 could also bereversed. The oblong hole 11 allows the upper part 2 of the surround 1to hold several different relative positions with respect to the lowerpart 3 of the surround 1. To increase the area over which the clampingscrew 12 bears on the oblong hole 11, a washer 13 of sufficient size isarranged between the clamping screw 12 and the oblong hole 11. The axisof clamping s is orthogonal to the plane of FIG. 3.

[0020]FIG. 4 schematically depicts a sectioned view of anotheradvantageous detail regarding the device for clamping the parts of thesurround of a device involving an appreciably flat element heldmechanically by a system according to the invention. The axis ofclamping s of the clamping screw 12 is depicted. The outer surface 10 ofthe upper part 2 of the surround 1 has a depression 14 arranged towardthe inside of the device, that is to say toward the appreciably flatelement, that is to say, in this instance in FIG. 4, toward the lowerpart 3 of the surround 1. The clamping device is depicted without awasher in FIG. 4.

[0021] The square-section elastic gaskets of the devices according tothe prior art make it possible to absorb significant variations intolerance but have the disadvantage of allowing significant movements ofthe appreciably flat element in its mean plane. Now, the problems ofsignificant variations in tolerance being settled by the differentrelative positions of the parts of the surround one with respect to theother in a direction roughly orthogonal to the mean plane of the elementwhich are allowed in a device according to the invention. In order tolimit the movements of the appreciably flat element in its mid plane,the elastic gasket or gaskets used in the device according to theinvention are preferably flat gaskets. A flat gasket is a gasket thewidth of which is at least twice its thickness. A flat gasket is morestable than a square gasket, that is to say than a gasket with a squarecross section. The width of the flat gasket used is advantageouslyroughly three times the thickness of said flat gasket. In a preferrednumerical example, the width of the flat gasket is about 2.5 mm whileits thickness is about 0.8 mm. Each elastic gasket is advantageouslymade of silicone.

[0022] In a preferred embodiment there is at least one gasket betweenthe appreciably flat element and each part of the surround, as in FIG. 2for example. For example; when the gaskets are placed at the peripheryof the appreciably flat element, on each side of the appreciably flatelement, there may be either a single gasket running all around theappreciably flat element in the mean plane of the appreciably flatelement or alternatively several sections of gasket, that is to say infact several gaskets arranged along the periphery of the appreciablyflat element. In another embodiment, there is at least one gasketbetween the appreciably flat element and one of the parts of thesurround, while there is a plastic film, advantageously a self-adhesiveone, between the appreciably flat element and the other part of thesurround. As a preference, the first part is the upper part 2 while thesecond part is the lower part 3, this being so as to afford bettersealing of the inside of the device which is situated under theappreciably flat element 4 in FIG. 2.

[0023] When the device according to the invention is being mounted, themounting method preferably involves a step of trapping the element bycompression of the gasket or gaskets by applying a nominal force untilthe nominal force is balanced by the opposing force supplied by thecompressed gasket or gaskets. Thus, the holding force exerted by theparts of the surround on the appreciably flat element via the gaskets isfully controlled. The relative movement of the parts of the surround onewith respect to the other is preferably in sliding along a contactsurface for contact between the parts of the surround, the contactsurface being roughly orthogonal to the mean plane of the appreciablyflat element so as not to apply to the gasket or gaskets transverseforces, that is to say forces in directions belonging to the mean planeof the appreciably flat element. When the nominal force is beingapplied, the parts of the surround which come closer together do notbutt against each other along a contact surface parallel to the meanplane of the appreciably flat element, and this is so as to be able touse all the intended range of various relative positions of the parts ofthe surround.

[0024] The invention may advantageously be applied to aircraft consoles.An aircraft console uses one or more display devices involving one ormore liquid crystal screens.

1. A device comprising at least: an appreciably flat element (4); asurround (1) intended to receive the element (4), the surround (1)comprising two parts (2, 3) intended to trap a portion of the element(4) between them in a direction (Y) roughly orthogonal to the mean plane(XZ) of the element (4) via at least one elastic gasket (7, 8); amechanical system for holding the relative position of the parts (2, 3)of the surround (1), one with respect to the other; characterized inthat the parts (2, 3) of the surround (1) and the mechanical holdingsystem are structured and arranged in such a way as to be able to holdseveral relative positions of the parts (2, 3) of the surround (1), onewith respect to the other, in a direction (Y) roughly orthogonal to themean plane (XZ) of the element (4), and in that the mechanical holdingsystem is a clamping device, the axis of clamping (s) of which isroughly orthogonal to the axis of compression (Y) of the elastic gasketor gaskets (7, 8).
 2. The device as claimed in claim 1, characterized inthat the various relative positions cover at least one continuous range.3. The device as claimed in either one of the preceding claims,characterized in that the device is a display device and in that theappreciably flat element (4) is an appreciably flat display cell.
 4. Thedevice as claimed in claim 3, characterized in that the appreciably flatdisplay cell (4) is a liquid crystal screen.
 5. The device as claimed inany one of the preceding claims, characterized in that the parts (2, 3)of the surround (1) together, in the held position, exhibit at least onecontact surface (SC) roughly orthogonal to the mean plane (XZ) of theelement (4).
 6. The device as claimed in any one of the precedingclaims, characterized in that the mechanical holding system is aclamping device comprising at least one screw (12) sliding in an oblonghole (11).
 7. The device as claimed in claim 6, characterized in thatthe clamping device comprises a washer (13) arranged between the screw(12) and the oblong hole (11), the washer (13) being large enough toincrease the area over which the screw (12) bears against the oblonghole (11).
 8. The device as claimed in either one of claims 6 and 7,characterized in that the oblong hole (11) lies in a depression (14)which is located in an outer surface (10) of the surround (1) and whichis arranged toward the inside of the device.
 9. The device as claimed inany one of the preceding claims, characterized in that the two parts (2,3) of the surround (1) each have a surface (S2, S3) facing the otherpart, each of said surfaces (S2, S3) having a stepped profile.
 10. Thedevice as claimed in any one of the preceding claims, characterized inthat the gasket (7, 8) is a flat gasket, the width (1) of the flatgasket (7, 8) being at least twice the thickness (e) of the flat gasket(7, 8).
 11. The device as claimed in claim 10, characterized in that thewidth (1) of the flat gasket (7, 8) is roughly three times the thickness(e) of the flat gasket (7, 8).
 12. The device as claimed in any one ofthe preceding claims, characterized in that the gasket (7, 8) is made ofsilicone.
 13. The device as claimed in any one of the preceding claims,characterized in that there is at least one gasket (7, 8) between theelement (4) and each part (2, 3) of the surround (1).
 14. The device asclaimed in any one of claims 1 to 12, characterized in that there is atleast one gasket (7) between the element (4) and the first part (2) ofthe surround (1) and there is a plastic film between the element (4) andthe second part (3) of the surround (1).
 15. The device as claimed inany one of the preceding claims, characterized in that the mechanicalholding system is demountable.
 16. A method for mounting a device asclaimed in any one of the preceding claims, characterized in that themethod involves a step of trapping the element (4) by compression of thegasket or gaskets (7, 8) by applying a nominal force until the nominalforce is balanced by the opposing force supplied by the compressedgasket or gaskets (7, 8).
 17. The mounting method as claimed in claim16, characterized in that the relative movement of the parts (2, 3) ofthe surround (1) one with respect to the other is in sliding along acontact surface (SC) for contact between the parts (2, 3) of thesurround (1), the contact surface (SC) being roughly orthogonal to themean plane (XZ) of the appreciably flat element (4).
 18. The mountingmethod as claimed in either one of claims 16 to 17, characterized inthat when the nominal force is being applied, the parts (2, 3) of thesurround (1) which come closer together do not butt against each otheralong a contact surface parallel to the mean plane (XZ) of theappreciably flat element (4).
 19. An aircraft console characterized inthat it comprises at least one display device as claimed in any one ofclaims 3 to 15, or at least one display device mounted using themounting method as claimed in any one of claims 16 to 18.